Rice (i.e. Oryza sativa) is recognized to be an important food crop in many parts of the world. However, heretofore rice production has not benefited to a substantial degree from heterosis or hybrid vigor made possible when different parental lines are cross-pollinated. For a number of reasons primarily related to the unique rice plant morphology, the controlled cross-pollination of rice plants has been difficult to achieve on a commercial scale.
Representative articles which discuss hybrid rice production are:
(1) "Hybrid Rice--Problems and Potentials", by J. W. Stansel and J. P. Craigmiles, Rice Journal, Vol. 69, No. 5, Pages 14 to 15, and 46 (1966). PA1 (2) "Outlook for Hybrid Rice in the USA", by H. L. Carnahan, J. R. Erikson, S. T. Tseng, and J. N. Rutger, Rice Breeding, International Rice Research Institute, Laguna, Philippines, Pages 603 to 607 (1972). PA1 (3) "Outlook for Hybrid Rice in India", by M. S. Swaminathan, E. A. Siddig, and S. D. Sharma, Rice Breeding, International Rice Research Institute, Laguna, Philippines, page 609 to 613 (1972). PA1 (4) "Current Status and Future Prospects for Breeding Hybrid Rice and Wheat", S. S. Virmani and Jan B. Edwards, Advances in Agronomy, Vol. 36, Pages 145 to 214 (1983). PA1 (5) "A Concise Course in Hybrid Rice", by Long P. Yuan, Hunan Science and Technology Publishers, Hunan, China, Pages 1 to 168 (1985). PA1 (6) "Current Status of Hybrid Rice Research and Development", by L. P. Yuan and S. S. Virmani, International Symposium on Hybrid Rice, Changsha, Hunan, China, Pages 1 to 16 plus tables (1986). PA1 (a) growing in a planting area a population of (i) perennial female fertile male sterile rice plants, and a population of (ii) annual female fertile male fertile rice plants which are capable of restoring male fertility to plants in the next following generation resulting from the pollination of population (i) by population (ii), PA1 (b) pollinating the population (i) with pollen derived from the population (ii) whereby seeds are formed on the plants of population (i) which are capable of forming annual male fertile F.sub.1 hybrid Oryza sativa plants and seeds are formed on the plants of population (ii) as the result of self-pollination, PA1 (c) harvesting the seeds which have formed on the plants of populations (i) and (ii), PA1 (d) retaining the plants of population (i) through the following winter in the substantial absence of irrigation while exposed to ambient conditions with the retention of substantial viability and killing the plants of population (ii) while exposed to such conditions, PA1 (e) planting in the planting area during the next subsequent growing season an additional population of (ii) annual female fertile male fertile rice plants which are capable of restoring male fertility to plants resulting from the pollination of the surviving plants of population (i) by the additional population (ii), PA1 (f) pollinating the plants of the surviving population (i) with pollen derived from the plants of the additional population (ii) whereby seeds are formed on the plants of the surviving population (i) which are capable of forming annual male fertile F.sub.1 hybrid Oryza sativa plants, and PA1 (g) harvesting the seeds which have formed on the surviving population (i) and the additional population (ii).
In Long P. Yuan U.S. Pat. No. 4,305,225, techniques are disclosed for aiding the production of hybrid rice. For instance, the male sterile seed parent plants can be sprayed with a growth hormone (e.g., gibberellin) in order to cause the flower-bearing panicles to more fully emerge from the rice leaf sheath. Any portion of the panicle which does not emerge will be incapable of receiving pollen from the pollen parent and thereby diminishes the yield of seeds capable of forming F.sub.1 hybrid rice. The application of the growth hormone adds a significant expense to the overall process.
In J. Neil Rutger et al U.S. Pat. No. 4,351,130 a rice hybridization process is disclosed wherein the male pollinator plants are recessively inherited tall plants.
In Zoltan Barabas U.S. Pat. No. 3,842,538 is disclosed a hybrid seed production process wherein hybrid grains and pure grains are separated on the basis of color. Unlike wheat and similar grains, rice grains possess an outer hull which if removed will normally reduce their viability for planting purposes.
Heretofore, rice production has been carried out in the Peoples Republic of China using a highly labor intensive technique wherein the male and female rice parents are first seeded separately at different times in different beds, transplanted to different adjoining areas, monitored for growth on a weekly basis by observing the leaf count, the rate of growth is adjusted by water and fertilizer management, a growth hormone such as gibberellin is applied to the seed parent plants in order to cause the flower panicles to be more fully exserted out of the leaf sheath, the flag leaves of the seed parent plants are clipped, if wind currents are deficient pollen sometimes is transferred by hand through the movement of a rope across the planting area, and the seeds which are capable of forming F.sub.1 hybrid rice plants are selectively harvested.
In Alfonso G. Calub U.S. Pat. No. 4,764,643 is disclosed an improved economically feasible procedure for forming Oryza sativa plants wherein the requisite parent plants possess a novel combination of certain specified properties. Such process requires the use of three different plant lines, i.e., (1) cytoplasmically male sterile rice plants, (2) maintainer plants to make possible the increase of the cytoplasmically male sterile plants, and (3) restorer plants to impart male fertility to the resulting F.sub.1 Oryza sativa plants. The use of the maintainer plants and the annual planting of the two parent plants adds to the overall cost of the hybrid rice product. The present invention represents an improvement over such technology.
Also, during the last five years Chinese scientists have developed an additional approach to hybrid rice production which is commonly called the "two-line system". In this system, photoperiod sensitive genetic male sterile rice plants are utilized with restorer rice plants. When less than approximately fourteen hours of daylight are experienced, the photoperiod sensitive rice plants behave as maintainer plants, and when the light is more than approximately fourteen hours per day, the photosensitive rice plants exhibit male sterility. Accordingly, in theory the photoperiod sensitive rice plants can form seeds via self-pollination in the fall which can be planted to form male sterile rice plants in the spring. One thus avoids the necessity of increasing the male sterile plants by the tedious and time-consuming planting of the same in uniform populations adjacent maintainer plants coupled with the selective harvest of the seeds formed on the male sterile plants. However, it is understood that such technology at this stage relies not only on the length of daylight but also is significantly affected by variability in temperature which cannot be controlled. Hence, the reliability of the two-line system is still highly questionable.
It is an object of the present invention to provide an improved process for forming seeds capable of forming male fertile F.sub.1 Oryza sativa plants on an ongoing basis which is capable of being readily implemented on a commercial scale.
It is an object of the present invention to provide an improved process for forming seeds capable of producing male fertile F.sub.1 hybrid Oryza sativa plants on an ongoing basis which eliminates the annual expense of increasing the seeds required to plant the male sterile rice parent plants.
It is an object of the present invention to provide an improved process for forming seeds capable of producing male fertile F.sub.1 hybrid Oryza sativa plants on an ongoing basis wherein the provision of the required male sterile parent plants is handled in a highly efficient manner.
It is an object of the present invention to provide an improved process for forming seeds capable of producing male fertile F.sub.1 hybrid Oryza sativa plants on an ongoing basis wherein the planting of male sterile parent plants is not required at the beginning of every growing season.
It is an object of the present invention to provide an improved process for forming seeds capable of producing male fertile F.sub.1, hybrid Oryza sativa plants on an ongoing basis wherein there is a significantly reduced labor requirement.
It is a further object of the present invention to provide an improved process for forming F.sub.1 Oryza sativa plants on an ongoing basis which can be carried out on a reliable and economically attractive basis with a significant reduction in production costs.
It is a further object of the present invention to provide novel improved Oryza sativa seed products which are useful in the establishment of the male sterile parent plants which are used in F.sub.1 hybrid seed production.
It is another object of the present invention to provide novel improved male sterile Oryza sativa plants which are useful in F.sub.1 hybrid seed production.
These and other objects as well as the scope, nature and utilization of the claimed invention will be apparent to those skilled in the art from the following detailed description and appended claims.